The present invention relates to improvements in a measuring and controlling apparatus for a flow rate of powder carried by gas.
Heretofore, as the above-described type of apparatus, an automatic powder feeding apparatus invented by one of the inventors of this invention, for which a patent application was filed (See Japanese Patent Application No. 60-204978), comprising a nozzle for blowing a carrier fluid into an inlet of a detector tubular passageway having an inlet and an outlet, means for detecting a pressure difference between an inlet side pressure detecting port provided upstream of the outlet of the nozzle and an outlet side pressure detecting port provided at the outlet of the detector tubular passageway, means for shunting apart of the carrier fluid to the inlet side pressure detecting port and regulating a pressure at the outlet of the detector tubular passageway, means for regulating a pressure at the inlet of the detector tubular passageway, the means for regulating a pressure at the outlet of the detector tubular passageway being an injector connected via a valve to that outlet, and an automatic control valve having the pressure difference applied as its input and a flow rate of a driving fluid of the injector issued as its control output and including means for presetting a set value corresponding to the pressure difference, has been known.
This apparatus in the prior art will be explained in more detail with reference to FIG. 7, as follows.
There is provided a sensor nozzle 3 for feeding a carrier gas into a detector tubular passageway 1, and a carrier gas having its flow rate regulated by a valve 16 is introduced thereto through a carrier gas feed port 5. In addition, an inlet pressure detecting port 6 opens upstream of a sensor nozzle port 4 of the sensor nozzle 3, and a part of the carrier gas having its flow rate controlled by a valve 16' is fed to that port 6 via an inlet side fluid resistance 14 and through a tubular passageway 12. In this instance, as shown in FIG. 7, a flow meter 17 is connected in such manner that a total flow rate of a carrier gas which flows through a valve 16 and the valve 16' and is finally blown into the detector tubular passageway 1 having been joined together through the sensor nozzle port 4, can be measured. As shown in the figure, a sensor tube 2 is supported coaxially with the sensor nozzle 3 and fixed in position in the axial direction by a sensor body 10. A powder layer 51 in a tank 50 is fluidized by gas 54 fed through a perforated plate 52 disposed at the bottom of the tank 50 as shown by arrows 53, and the powder in the powder layer 51 is introduced through a powder introducing pot 7 towards an inlet 8 of the detector tubular passageway 1 between the sensor tube 2 and the sensor nozzle 3. The sensor body 10 is fixedly mounted to the tank 50. At an outlet 9 of the sensor tube 2 is opened an outlet side pressure duct 13, and a predetermined gas is adapted to be introduced to this outlet 9 via an outlet side fluid resistance 15 as controlled by an outlet pressure shift valve 18. It is to be noted that reference numeral 26 designates a diaphragm type differential pressure gauge, and this gauge is adapted to detect a difference between the pressures at the detector tubular passageway outlet 9 and at the detector tubular passageway inlet 8, which are respectively picked up in the outlet side pressure duct 13 and in the inlet pressure detecting port 6 and applied to the differential pressure gauge through a differential pressure gauge lower pressure duct 20 and a differential pressure gauge higher pressure duct 19, respectively. The pressure difference detected by the differential pressure gauge 26 in the above-described manner, is a pressure difference generated in the process in which powder is introduced through the powder introducing port 7 into the detector tubular passageway 1 and is accelerated by a carrier gas blown into the detector tubular passageway 1 through the sensor nozzle port 4. In addition, to the outlet 9 of the sensor tube 2 is connected an injector 46 via a valve such as a pinch rubber 49 or the like.
This pinch rubber 49 is contained in a pinch valve body 48 and communicates with a pressurizing hole 55 drilled in the pinch valve body 48. By charging and discharging pressurized air through the pressurizing hole 55, the passageway inside of the pinch rubber 49 can be closed and opened, respectively. In FIG. 7, a pinch rubber 49a depicted by dash-dot lines shows a closed state of the pinch rubber 49 as a result of elastic deformation.
In this powder flow rate measuring apparatus, in the case where it is desired to change a flow rate of powder, it is achieved by changing a flow rate of a driving gas 47 in an injector 46 which consists of an injector nozzle 41 and an injector throat 42, and by adjusting a degree of vacuum at the outlet 9 of the detector tubular passageway 1. In the event that a transporting speed of powder is too low in a transporting pipe 44 at the injector outlet, an appropriate transporting speed could be realized by providing a carrier gas adjusting duct 43 at the outlet of the injector throat 42 and introducing an additional gas through this duct 43. In this case, a flow rate of the additional carrier gas can be set by means of a carrier gas adjusting valve 36. A control valve 38 is a control valve used for the purpose of maintaining a powder flow rate detected by a powder flow rate measuring apparatus in the prior art at a predetermined constant value. More particularly, the control valve 38 operates in such manner that it compares a difference between the pressures introduced, respectively, through a control valve lower pressure duct 22 and a control valve higher pressure duct 23 with a preset value stored therein, it amplifies the pressure difference by means of a diaphragm contained therein. As a result it converts a source pressure applied through a control valve source pressure duct 35 and controlled at a fixed value into the driving gas 46, and it feeds the driving gas 47 to the injector 46. In addition, a control valve constant pressure duct 24 is a duct for introducing into the control apparatus a constant pressure which is necessary for the control valve to precisely amplify a minute gas pressure difference and reveal its function. Also, a valve 25 is a powder flow rate setting valve for making a constant pressure gas given by a constant pressure valve 29 flow through a fluid resistance 21 and for adding a pressure to the pressure at the inlet side pressure detecting port 6 that is given by the duct 19, for the purpose of setting. As controlled by this powder flow rate setting velve 25, a constant minute flow rate of gas passes through a powder flow rate setting fluid resistance 21, then passes through the differential pressure gauge higher pressure duct 19, and after passing through the inlet side fluid resistance 14, it joins with a carrier gas blown into the detector tubular passageway 1 through the sensor nozzle 3. Hence essentially it is a part of a carrier gas and could be fed in parallel to the valves 16 and 16', but since this flow rate is always constant, the gas feed piping connection could be made as shown in FIG. 7.
The operation of this control valve 38 is such that in the case where a level of fluidized powder 51 of the powder in the tank 50 has changed as, for instance, the flow rate of the powder has decreased, the control valve 38 acts to increase the flow rate of the driving gas 47 fed to the injector nozzle 41 and thereby restore the powder flow rate to the original value. On the contrary, in the case where the powder flow rate has increased, a degree of vacuum in the injector is lowered by reducing the flow rate of the driving gas 47, and thereby the powder flow rate may be automatically held constant.
This control valve 38 consists of a control valve higher pressure chamber 70 on the upper side and a control valve lower pressure chamber 67 on the lower side with a diaphragm 68 intervening therebetween, and a central portion of the diaphragm 68 is reinforced by center plates 69. Under the control valve lower pressure chamber 67 is provided a control valve body 60, and a control valve source pressure gas 80 having a precisely controlled constant pressure is introduced through the bottom of the body 60 via the duct 35. In the upper portion of the control valve body 60, a control valve main shaft 63 is fitted along a center axis of the control valve body 60 so as to be slidable in the vertical directions as opposed to a control valve port 61, the upper portion of the control valve main shaft 63 transforms to a thin control valve auxiliary shaft 64, whose tip end connects to the center plate 69, and a flow rate of the source pressure gas in the control valve is controlled through a narrow gap between the entire circumference of the bottom surface of the control valve main shaft 63 and the control valve port 61 so that the source pressure gas may pass through a control valve output chamber 62 and may flow out from a control valve output chamber 39 as shown by an arrow 81. It is to be noted that reference numerals indicated in FIG. 7 and identical to those given to component parts shown in FIG. 1 which will be described later, designate component parts having the same names and the same functions.
When the above-described apparatus in the prior art is stopped from its operating state, if the pinch rubber 49 is closed as described above, then a flow of carrier gas passing through the detector tubular passageway 1 towards the outlet 9 will stop and at the same time a flow of purging gas passing through the fluid resistance 15 and the outlet pressure introducing tube 13 towards the outlet 9 will also stop, so that the pressure within the outlet 9 will rise quickly.
This quickly rising pressure raises the pressure in the control valve lower pressure chamber 67 via the outlet pressure introducing tube 13 and the control valve lower pressure duct 22, hence the diaphragm 68 and the control valve shaft 63 integrally coupled thereto are pushed up to make the control valve port 61 largely open the gap at its bottom. As a result, a flow rate of the source pressure gas flowing from the control valve source pressure duct 35 to the control valve output duct 39 increases, so that the source pressure gas is ejected from the injector nozzle 41 at a high speed, and a degree of vacuum at this portion is raised abnormally.
Under this condition, if the pinch rubber 49 is opened for the purpose of commencing the operation, then the pressure in the outlet 9 will be lowered quickly, so that the fluidized powder 51 in the tank 50 is sucked at a large rate through the detector tubular passageway 1, and thereby the flow rate of the powder is quickly increased.
In this way, the carrier gas and the powder begin to flow through the detector tubular passageway 1 towards the outlet 9, and in addition, when a purging gas begins to flow through the outlet presssure introducing tube 13 towards the outlet 9, the pressure at the outlet 9 is lowered quickly, and the flow rate of the powder flowing through the detector tubular passageway 1 returns to a normal state value.
Thereafter, if the pinch rubber 49 is closed again, the flow rate of the powder becomes zero and the pressure at the outlet 9 rises in the above-described manner.
The variation with time of the powder flow rate at this time is shown in FIG. 8. In this figure, the state where the powder flow rate is zero when the pinch rubber 49 is closed and the operation is stopped is shown at Q.sub.1. The powder flow rate immediately after the pinch rubber 49 in a closed condition has been opened, is shown at Q.sub.2. In addition, the powder flow rate during a normal operation is shown at Q.sub.3.